A machine tool is known from DE 601 11 162 T2 (equivalent to EP 1 208 940 B1) comprising a tool carousel for machining metallic workpieces. The tool carousel comprises several chucks, in which one tool each is arranged for processing the workpiece. Cryogenic coolant is guided through the tool carousel to the respective tool presently engaged with the workpiece to be processed. High productivity in processing workpieces is yielded by the effective cooling using said cryogenic coolant.
The invention is based on the objective to provide a method allowing higher productivity in machining metallic workpieces.
Using the method according to the invention, the productivity in processing workpieces is increased such that during processing of the workpiece by a first tool, a second tool provided for a subsequent processing is precooled by the cryogenic coolant simultaneously during processing. For the cryogenic processing of workpieces the tools first need to be cooled to the required low operating temperature before the machining process can begin. This cooling process for the cryogenic processing of workpieces can only begin in methods and machine tools of prior art when the tool provided for processing is located in the operating position and/or in the chuck provided for processing. For example, the cooling process in methods and machine tools of prior art can only begin when the tool provided for processing is located in the tool spindle connected to a supply line for the cryogenic coolant.
Due to the fact that as early as during the processing of the workpiece via a first tool the second tool provided for subsequent processing is being cooled by the cryogenic coolant, the precooling period required for the second tool is moved from the primary processing time into the secondary processing time. Due to this precooling simultaneous to the primary processing time, the workpiece, after being processed by the first tool, can directly be further processed without any additional precooling by the already precooled second tool. This way, no primary processing time is lost, in which the second tool had to be cooled to the lower processing temperature. The cryogenic processing of a workpiece can therefore be continued directly after the change of tools, with the second tool during processing being cooled by the cryogenic coolant.
The precooling of a tool provided for subsequent processing occurs for example via a precooling device, which can be coupled to a tool magazine, a tool carousel, or any other chuck.
The method ensures a simple and effective precooling of the second tool provided for processing. For example, liquid or gaseous nitrogen, liquid or gaseous oxygen, gaseous hydrogen, gaseous helium, liquid or gaseous argon, gaseous carbon dioxide, and liquid or gaseous natural gas may serve as the cryogenic coolant. Preferably, during processing, the same cryogenic coolant is used, preferably nitrogen, for the precooling and the subsequent cooling of a workpiece.
The method ensures a rapid and effective precooling of the tool provided for subsequent processing. Preferably the cryogenic coolant provides the lower temperature even when it hits and/or flows through the workpiece to be precooled.
The method ensures that the processing of the workpiece can be continued immediately after the change of tools. The change of tools may occur, for example, by the precooled second tool being changed into the first chuck, which may be embodied as a tool spindle, for example. Alternatively the change of tools can occur by the second chuck with the second tool held there and precooled being moved from a storage position into a processing position. This is the case, for example, in tool carousels, with the different tools being brought by way of rotation of the carousel disk from a storage position into the processing position. The precooling device is particularly embodied such that the tool exchange occurs so fast that the second tool provided for processing essentially does not heat up prior to the change into the processing position.
The method ensures an efficient precooling of the tool provided for processing.
The method allows precooling in a simple fashion. The precooling device comprises for example a thermally isolated reservoir for providing the cryogenic coolant and a corresponding cooling condenser for cooling the cryogenic coolant as well as a precoolant-feeding line to supply the cryogenic coolant from the reservoir to the second chuck. The precoolant supply line is preferably embodied in a thermally isolated fashion. Preferably the precoolant device is coupled to a cryogenic cooling device to cool the tools during processing such that for precooling and for cooling during processing, the cryogenic coolant is taken from the same reservoir.
The method ensures in a simple fashion that during the change of tools no cryogenic coolant escapes the precooling device in an uncontrolled fashion. This way, a long operating life of the machine tool is ensured because cryogenic coolant only flows out of the precooling device when a tool to be precooled is coupled thereto.
The method ensures a simple and efficient cooling of the tool provided for processing. The influx of cryogenic coolant is only released by the precooling device when the tool to be precooled is coupled to the precooling device.
The invention is further based on the objective to further develop a machine tool of the generic type such that an increase of productivity is yielded in the machining of metallic workpieces.
The advantages of the machine tool according to the invention are the same as the above-described advantages of the method according to the invention. The machine tool according to the invention comprises a cooling device for the cryogenic cooling of the first tool, which is presently engaging the workpiece to be processed. Furthermore, the machine tool comprises a precooling device, serving to precool a second tool provided in a second chuck and intended for the subsequent processing of the workpiece. The cryogenic cooling device and the cryogenic precooling device are addressed by a control device such that during processing of the workpiece by a first tool the second tool provided for the subsequent processing of the workpiece is precooled and brought to the lower processing temperature required. This way, in the above-described manner, the precooling time for the second tool is changed from the primary processing time to the secondary processing time. After changing the second tool into the position intended for processing the workpiece the processing of the workpiece can continue immediately. This way, the primary processing time and/or cycle time for the tool processing is reduced and the productivity of the machine tool is increased.
The machine tool ensures a simple precooling of the tool provided for processing. Preferably the reservoir and the corresponding cooling condenser are both part of the precooling device as well as a part of the cooling device, so that the cooling of the tool processing the workpiece and the precooling of the tool provided for processing can occur with the same cryogenic cooling medium. For this purpose, a precoolant-supply line leads from the reservoir to the second chuck and a coolant-supply line from the reservoir to the first chuck.
The machine tool ensures effective precooling of the tool provided for processing. The supply of the cryogenic coolant to the tool to be pre-cooled is only released when the tool is mechanically coupled to the coupling unit. The release of the cryogenic coolant can occur either mechanically or electromechanically.
The machine tool ensures in a simple fashion the coupling and decoupling of the precooling device to and/or from the second chuck. For this purpose, either the precooling device can be arranged fixed at a basic frame of the machine tool and the second chuck can be displaceable or vice versa.
The machine tool ensures the precooling of a multitude of different tools in a simple fashion. The first chuck may be embodied as a common tool spindle, for example, which performs a tool exchange in the pick-up method and here places the first tool into the tool magazine and accepts the precooled second tool from the second chuck. Alternatively, a common tool changer may be used.
The machine tool ensures an efficient precooling and simultaneously an efficient cooling during processing. The reservoir is both a part of the precooling device as well as a part of the cooling device so that only one reservoir is required in order to guide the cryogenic coolant via the precoolant-supply line to the second chuck and via the coolant supply line to the first chuck.
The machine tool ensures efficient precooling and cooling of the respective tool. The supply lines preferably show a specific thermal conductivity at 0° C. of maximally 0.40 W/(mK), particularly no more than 0.30 W/(mK), and particularly no more than 0.20 W/(mK). By a thermally isolated embodiment any undesired heating of the cryogenic coolant is prevented over the path from the first and/or the second chuck. This way, the respective tool can be precooled and/or cooled extremely effectively. Preferably the supply lines are embodied entirely in a thermally insulated fashion, i.e. over their entire length. Furthermore, the supply lines are preferably embodied in a vacuum-isolated fashion. For this purpose they comprise an inner tube and an outer tube surrounding it, connected to each other and limiting an evacuated isolated space. In the vacuum-isolated embodiment the supply lines preferably show a specific thermal conductivity at 0° C. of no more than 0.01 W/(mK). In a vacuum-isolated embodiment preferably at least one of the tubes can be changed in its length so that a compensation to different longitudinal changes of the inner and the outer tube is possible. When the supply lines conduct the cryogenic coolant the respectively inner tube essentially assumes its temperature, while the respectively outer tube, based on the isolation medium arranged between the two tubes, cools considerably less. The inner tube changes its length therefore to a considerably greater extent than the outer tube. In order to avoid any damage to the supply lines at least one of the tubes is capable of changing its length. Preferably the outer tube comprises a pleated metallic bellows for a thermal compensation of length.
Additional features, advantages, and details of the invention are discernible from the following description of an exemplary embodiment.